I think there are two distinct things in play here.Quote:
Originally Posted by maloufn
The technical part is, that every printing technology has a 'native' resolution at which it prints: often the (in)famous 300 ppi (note, not dpi, that's a different beast altogether). Any different resolution than that will have to be converted before printing. This is exactly the same as preparing a picture for screen viewing (at low resolution), so theoretically the same rules should apply (good, but slow, algorithm and output sharpening). In practice, you won't see the difference in 'normally made' image (as Colin said).
That was pure technical/theoretical.
For viewing, what counts is not spatial resolution, but angular resolution. Humans can view details down to (the order of) 0.1mm at 30 cm (say 300 ppi ;) ). Viewing something from 10x that distance, at 3 m, details smaller than 1 mm would be invisible, so that's the optimal print resolution for that viewing distance (equivalent to 30 ppi).
So the larger the viewing distance, the lower the required ppi for a print to be considered excellent.
As for the texture of the support: any texture tends to hide the small detail, so no need to print that small detail, so you won't see the difference between 300 and 180 ppi.
So for printing: basically, no need to worry about your resolution, unless you crop your original image (and even then there's quite a margin)
Note that I'm just repeating what Colin said before, just rephrased and expanded the viewing distance bit.
Regards,
Remco
As a side note, there are professionals that don't understand ppi etc. either: a shop where I wanted to get some 6x4 prints claimed I didn't have the proper image ratio, only because pixel sizes were not those calculated from printer resolution...